Using Archived AVL-APC Data to Improve Transit Performance and Management (2006) / Chapter Skim
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From page 54... ...
, and sampling error. It is also important to distinguish between the accuracy of raw counts and that of screened and corrected counts, and between the accuracy of directly measured items (ons and offs by stop)
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One example is a route that ends with a loop; another example is a pair of interlined routes for which nominally transferring passengers actually remain on board. Data structures have to identify which route ends are not necessarily zero-load points and recognize passengers inherited from a previous trip.
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The Overlapping Loop Model for Short Loops A third approach, used by NJ Transit on its Philadelphia routes (38) , is to model a bus in a loop as serving two trips at once, attributing alightings to the trip entering the loop and boardings to the trip exiting the loop.
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Attributing Alightings Trip Entering Trip Leaving Figure 19. Overlapping loop model.
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Besides achieving on-off balance, corrections aim to prevent negative loads. The algorithms the researchers have seen consider only departing load.
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8.3.3 Correcting Negative Loads After a sub-block is balanced, calculated loads may be negative at one or more points along a route. Most commonly checked is departing load; however, a stronger test is for through load (departing load minus ons)
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Balance Offs (c) Check for negative load (continued on next page)
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Check for Neg Load, Early Subblock Input Ons Cum Ons Scaled Cum Round'd Cum Bal'c'd Ons 1 12 12 12.96 13 13 2 7 19 20.52 21 8 3 6 25 27.00 27 6 4 0 25 27.00 27 0 5 25 27.00 27 0 Total 25 f = 27 Target 27 1.080 Stop Input Ons Cum Ons Scaled Cum Round'd Cum Bal'c'd Ons 5 2 2 1.60 2 2 6 5 7 5.60 6 4 7 2 9 7.20 7 1 8 0 9 7.20 7 0 9 1 10 8.00 8 1 10 10 8.00 8 0 Total 10 f = 8 Target 8 0.800 Stop Offs Ons Thru Load Dep Load 1 13 0 13 2 2 8 11 19 3 4 6 15 21 4 9 0 12 12 5 13 2 -1 1 6 0 4 1 5 7 1 1 4 5 8 0 0 5 5 9 4 1 1 2 10 2 0 Total 35 35 Stop Input Offs Cum Offs Scaled Cum Round'd Cum Bal'c'd Offs 1 0 0.00 0 0 2 2 2 1.93 2 2 3 4 6 5.79 6 4 4 10 16 15.45 15 9 5 13 29 28.00 28 13 Total 29 f = 28 Target 28 0.966 Stop Input Offs Cum Offs Scaled Cum Round'd Cum Bal'c'd Offs 5 0 0.00 0 0 6 0 0 0.00 0 0 7 1 1 1.17 1 1 8 0 1 1.17 1 0 9 3 4 4.67 5 4 10 2 6 7.00 7 2 Total 6 f = 7 Target 7 1.167 Stop Offs Ons Thru Load Dep Load Violation 1 0 13 0 13 2 2 8 11 19 3 4 6 15 21 4 9 0 12 12 5 13 -1 Stop Offs Ons Thru Load Dep Load 1 0 1 0 1 2 0 0 1 1 3 0 0 1 1 4 -1 0 2 2 5 1 0 1 1 6 0 -1 1 0 7 0 -1 0 -1 8 0 0 -1 -1 9 1 0 -2 -2 10 0 -2 -2 Total 1 -1 Stop Offs Ons Thru Load Dep Load Violation 5 0 2 -1 1 6 0 4 1 5 7 1 1 4 5 8 0 0 5 5 9 4 1 1 2 10 2 0 0 0 Table 10. (Continued)
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Both segments, after balancing, have no negative load violations, so the correction procedure ends. 8.3.4 Other Count Correction Issues Independent of the balancing procedure, several questions related to databases and corrected counts arise: • Should the database store corrected counts, or should corrections be made on the fly?
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